Tea pickers at work in the Ugandan town of Ishaka last December. A BBC investigation found evidence that children are being exploited on land linked to the Catholic church in Uganda.
Photograph: Ivoha/Alamy

The distinction is not mere semantics. Child slavery is defined in the 1956 supplementary convention on slavery as the delivery by parents or guardian of a child to a third party for the purposes of exploitation. It is shocking to imagine that parents could ever hand over their child to be enslaved but I’ve seen parents do arguably worse things. When I first worked in Ethiopia during the early 1990s, I met a mother who was intentionally starving her infant son to death – she simply could not afford to feed her whole family.

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The particular features of child slavery have further implications. When we encounter child labour, however hazardous, it tends to be undertaken while the child is still under parental care. Generally, these parents will have the best interests of their child at heart – sometimes they may be profoundly mistaken as to what those best interests are – but it is a sad truth that in some of the most impoverished communities, child labour may be the best option available for children and their families.

So when engaging in the struggle to end child labour there is that potential commonality of purpose with parents who will often be open to new ideas about how to do better by their children. Working with communities to increase access to education for kids, and provide decent work for their parents, can therefore lead to a dramatic decrease in child labour.

No such potential exists in relation to child slavery. Consider for a moment children who have been delivered by their parents or guardians to be trafficked for sexual exploitation or as domestic workers, or who have been conscripted in armed conflicts, or utilised as forced labour by a third party, such as Uzbekistan’s slavery programme for cotton harvesting.

While these represent diverse practices that occur within a wide variety of different socio-economic contexts, they all have one thing in common: in not one of them, nor in any other child slavery situation, do the adults carrying out the exploitation of the children care for the best interests of the child.

In 2012, the International Labour Organisation estimated that there were 5.5 million children in slavery. This was exactly the same as the ILO’s estimate for 2005.

It is not surprising that the number of enslaved children has not decreased. Child slavery is not only poorly addressed but also poorly identified. In addition, child slavery is prized among some powerful vested interests in society. The tea industry and other agricultural supply chains thrive with the enslavement of children; not only cobalt, but coltan and gold are mined by child slaves; child abusepornography and the sexual trafficking of children are forms of slavery; and the blind acceptance of child marriage in many parts of the world ignores that it is, generally, the enslavement of children for sexual exploitation under the thinnest veil of respectability.

The failure to indict these practices for what they really are – slavery – betrays a misunderstanding not only of what is happening, but also why it is happening. This in turn saps urgency from political efforts to combat it. Further, it provides a modicum of protection for those who practise the enslavement of children; unchallenged, they continue to abuse with impunity.

The struggle to eradicate child slavery will be long and difficult. It shouldn’t be made harder by being overlooked every time it is encountered.